A self-oscillating resonant circuit is often used as an electrodeless lamp (i.e., fluorescent and high intensity discharge) ballast because of its simplicity and low cost. Disadvantageously, however, resonant circuits are, by the nature of their operation, very sensitive to variations in their components and the loads they are supplying. Hence, given typical component and lamp variations, the output power and efficiency of the ballast may not remain within desired relatively narrow limits.
Another problem, particularly for electrodeless fluorescent lamps operated as reflector lamps in "downlight" type fixtures (i.e., such that reflected light is emitted through a lower portion of the lamp opposite a reflective portion), the ambient temperature in which the lamp operates is relatively high because of the confined fixture space. Unfortunately, such high temperatures often approach the thermal limit for ballast components.
Accordingly, it is desirable to provide a simple and cost effective load network for a self-oscillating ballast configured such that the ballast is insensitive to component and lamp variations. Furthermore, it is desirable to improve the efficiency and reliability of the self-oscillating circuit by reducing stresses on its components, thus reducing operating temperature and extending the life of the ballast.